Adjustable interference progressive cavity pump/motor for predictive wear

ABSTRACT

Various examples are provided for progressive cavity pumps and motors. In one example, among others, a progressive cavity pump (or motor) includes a stator having a hyperboloidal internal bore including a plurality of spiral lobes, and a rotor comprising a plurality of spiral lobes positioned within the hyperboloidal internal bore of the stator. A longitudinal axis of the rotor is non-planar, non-parallel, and non-intersecting with a longitudinal axis of the stator. The stator can include an elastomeric material coating the hyperboloidal internal bore of the stator, which can reduce the effect of friction and abrasion during operation. The elastomeric material can include fluoro-based elastomers, other elastomeric materials or combinations thereof. For example, a fluoromonomer such as tetrafluoroethylene (TFE) or a fluoropolymer such as polytetrafluoroethylene (PTFE) can be used. The rotor can be configured to allow for displacement to adjust an interference fit between the rotor and the stator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to, and the benefit of, co-pending U.S.provisional application entitled “ADJUSTABLE INTERFERENCE PROGRESSIVECAVITY PUMP/MOTOR FOR PREDICTIVE WEAR” having Ser. No. 61/869,438, filedAug. 23, 2013, which is hereby incorporated by reference in itsentirety.

BACKGROUND

Progressive cavity pumps and/or motors are frequently used in oil fieldapplications for pumping fluids or driving downhole equipment in thewellbore. The progressive cavity mechanism includes a rotating gearmember and a stationary gear member. When designed according to thebasics of a gear mechanism of Moineau, and progressive cavity mechanismis generically known as a “Moineau” pump or motor. The progressivecavity mechanism can operate as a pump for pumping fluids or as a motorthrough which fluids flow to rotate the rotating gear member to producetorsional forces on an output shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present disclosure can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a cross-sectional view of an example of a progressive cavitypump and/or motor in accordance with various embodiments of the presentdisclosure.

FIG. 2 is a graphical representation of an example of a hyperboloidalconfiguration of a progressive cavity pump of FIG. 1 in accordance withvarious embodiments of the present disclosure.

FIG. 3 is a graphical representation of an example of a progressivecavity pump of FIG. 1 mounted in a wellbore in accordance with variousembodiments of the present disclosure.

DETAILED DESCRIPTION

Disclosed herein are various examples related to progressive cavitypumps and motors. Reference will now be made in detail to thedescription of the embodiments as illustrated in the drawings, whereinlike reference numbers indicate like parts throughout the several views.

A progressive cavity pump transfers fluid through the pump in a sequenceof small, fixed shape, discrete cavities that are defined by the rotorand stator of the pump. As the rotor is turned, the cavities move alongthe axial length of the pump. This produces a volumetric flow rate thatis proportional to the rotational speed. With low levels of shearingbeing applied to the pumped fluid, progressive cavity pumps haveapplications in, e.g., metering and pumping of viscous materials. Ingeneral, no pulsing of the fluid is produced by the progressive cavitypump. Progressive cavity pumps may also function as motors when fluid isforced through the interior of the motor. As such, descriptions withrespect to operation as a pump are equally applicable to operation as amotor.

Referring to FIG. 1, shown is a cross-sectional view illustrating anexample of a portion of a progressive cavity pump (or motor) 100. Theprogressive cavity pump 100 includes a stator 103 surrounding a rotor106. The stator 103 includes an outer portion and in inner portionformed of an elastomeric material 109. In some embodiments, the innerportion may be formed of a non-elastomeric material. The outer portionis generally fabricated using metal (e.g., steel or stainless steel),ceramic, or other composite materials, such as fiberglass, plastics,hydrocarbon-based materials and other structural materials, and mayinclude strengthening members, such as fibers embedded in the material,and forms the shell of the stator 103. Homogeneous materials aretypically utilized; however heterogeneous materials can also be used.The inner portion (or bore) of the stator 103 can include a coating ofan elastomeric material 109 forming spiral lobes (or gear teeth) withinthe stator cavity. The elastomeric material 109 is flexible and resistsabrasion. The elastomeric material 109 can include, e.g., rubber,Buna-N, nitrile-based elastomers, fluoro-based elastomers, Teflon™,silicone, plastics, other elastomeric materials or combinations thereof.The thickness of the coating of elastomeric material 109 can be in arange from about 1 mil to about 100 mil, or more. For example, thecoating thickness can be in a range from about 1 mil to about 50 mil,from about 1 mil to about 25 mil, from about 1 mil to about 20 mil, fromabout 1 mil to about 15 mil, or from about 1 mil to about 10 mil. Otherthicknesses of elastomeric material 109 may also be utilized.

In some cases, specially fabricated materials such as, e.g.,fluoropolymers (e.g., from DuPont) may be used to improve operation ofthe progressive cavity pump 100. Fluoropolymers can be prepared from atleast one unsaturated fluorinated monomer (fluoromonomer). Afluoromonomer suitable for use herein preferably contains about 35 wt %or more fluorine, and preferably about 50 wt % or more fluorine, and canbe an olefinic monomer with at least one fluorine or fluoroalkyl groupor fluoroalkoxy group attached to a doubly-bonded carbon. In oneembodiment, a fluoromonomer suitable for use herein istetrafluoroethylene (TFE).

An especially useful fluoropolymer is polytetrafluoroethylene (PTFE),which refers to (a) polymerized tetrafluoroethylene by itself withoutany significant comonomer present, i.e. a homopolymer of TFE, and (b)modified PTFE, which is a copolymer of TFE with such smallconcentrations of comonomer that the melting point of the resultantpolymer is not substantially reduced below that of PTFE (reduced, forexample, by about 8% or less, about 4% or less, about 2% or less, orabout 1% or less). Modified PTFE contains a small amount of comonomermodifier that improves film forming capability during baking (fusing).Comonomers useful for such purpose typically are those that introducebulky side groups into the molecule, and specific examples of suchmonomers are described below. The concentration of such comonomer ispreferably less than 1 wt %, and more preferably less than 0.5 wt %,based on the total weight of the TFE and comonomer present in the PTFE.A minimum amount of at least about 0.05 wt % comonomer is preferablyused to have a significant beneficial effect on processability. Thepresence of the comonomer is believed to cause a lowering of the averagemolecular weight.

The rotor 106 may be fabricated using metal (e.g., steel or stainlesssteel), ceramic, or other composite materials. Such materials aretypically homogeneous; however heterogeneous materials includingcomposites and/or new materials can also be used. The elastomericmaterial 109 comes in contact with spiral lobes (or gear teeth) of therotor 106 at contact points 112. As can be understood, contact betweenthe stator 103 and rotor 106 is a closed curve. In some embodiments, theouter portion of the rotor 106 can include a coating of the elastomericmaterial 109, which is flexible and resists abrasion. With the rotorcoated, the inner portion (or bore) of the stator 103 may or may notinclude a coating of an elastomeric material 109. The thickness of thecoating of elastomeric material 109 can be in a range from about 1 milto about 100 mil, or more. For example, the coating thickness can be ina range from about 1 mil to about 50 mil, from about 1 mil to about 25mil, from about 1 mil to about 20 mil, from about 1 mil to about 15 mil,or from about 1 mil to about 10 mil. Other thicknesses of elastomericmaterial 109 may also be utilized.

As FIG. 1 is a cross-sectional view, the contact points 112 are theintersection between the closed curve and an axial section. The numberof spiral lobes on the rotor 106 is less than the number of spiral lobeson the bore of the stator 103. For example, the rotor 106 may includefour spiral lobes and the stator 103 may include five spiral lobes. Thecontact between the stator 103 and rotor 106 defines the sealed cavitiesin which the fluid is transported through the progressive cavity pump100. At the contact points 112, the surfaces are generally travelingtransversely and axially. Areas or regions of sliding contact occur atcontact points along the closed curve. These areas are lubricated by thepumped fluid, which may include abrasive components. The elastomericmaterial 109 may include specialized materials to reduce the effects offriction and abrasion in high temperature and/or high pressureapplications such as, e.g., downhole mudpump operations in thepetrochemical industry.

The longitudinal axis of the rotor 106 is offset from the longitudinalaxis of the stator 103 and rotated by a defined angle to provide skewaxes. The defined angle can be greater than zero degrees and less than90 degrees. For example, the defined angle of rotation can be 0.5degree, one degree, or other small amount of angular rotation. Thedefined angle of rotation can be in a range from about 0.001 degree toabout 10 degrees, from about 0.005 degree to about 8.0 degrees, fromabout 0.01 degree to about 7.5 degrees, from about 0.05 degree to about5.0 degrees, from about 0.1 degree to about 3.0 degrees, about 0.2degree to about 2.0 degrees, from about 0.25 degree to about 1.5degrees, from about 0.3 degree to about 1.2 degrees, or from about 0.5degree to about 1.0 degree. In this way, the skew axes of the stator 103and rotor 106 are non-planar, non-parallel, and non-intersecting.

As with the defined angle, the offset of the longitudinal axis of therotor 106 from the longitudinal axis of the stator 103 can be a defineddistance that covers a wide range of values (e.g., about 0.01 inch ormore). For example, the defined distance can be in a range of about 0.01inch to about 10 inches, about 0.02 inch to about 10 inches, about 0.05inch to about 10 inches, about 0.05 inch to about 7.5 inches, about 0.05inch to about 5 inches, about 0.1 inch to about 5 inches, about 0.1 inchto about 2.5 inches, about 0.25 inch to about 2.5 inches, or otherranges as can be understood. The offset can be based upon the diameterof the stator 103. For example, an offset of about 0.5 inch can be usedfor a 10 inch diameter. In other embodiments, more or less offset can beutilized.

Rotation of the rotor 106 produces a circular movement about thelongitudinal axis of the stator 103. As the rotor 106 is rotated, theouter surface moves within the bore of the stator 103, which ishyperboloidal (e.g., generally shaped like a single surface hyperboloid)as illustrated in FIG. 2. The hyperboloidal internal bore of the stator103 exhibits a hyperboloidal shape for at least a portion of the axiallength of the stator 103. In the example of FIG. 1, the rotor 106axially tapers from a larger end to a smaller end. In other embodiments,the taper of the rotor 106 may also be hyperboloidal.

The spiral lobes of the stator 103 may be defined by a major diametercorresponding to the diameter at the bases of the spiral lobes and aminor diameter corresponding to the diameter at the peaks of the spirallobes. In contrast, the spiral lobes of the rotor 106 may be defined bya major diameter corresponding to the diameter at the peaks of thespiral lobes and a minor diameter corresponding to the diameter at thebases of the spiral lobes. Referring to FIG. 2, shown is a graphicalrepresentation of an example of the hyperboloidal configuration. In someimplementations, the applicable section 203 of the hyperboloid may bebelow the throat of neck 206 of the single sheet hyperboloid 200. Therotor axis 212 and the tangent line between the rotor and statorsurfaces 215 are non-planar, non-parallel, and non-intersecting skewlines. As can be understood, the dimensions of the spiral lobes varyalong the axial length of the progressive cavity pump 100. Thedimensions of the spiral lobes on the stator 103 can vary along theaxial length of the stator 103 as illustrated by the hyperboloidalsurfaces as illustrated by the hyperpoloidal stator pitch surfacesegment 209. The dimensions of the spiral lobes on the rotor 106 canvary based on the taper of the rotor 106. In some implementations, thespiral lobes on the rotor 106 may vary along the axial length of therotor 106 based upon the hyperboloidal taper.

Placement of the rotor 106 in the stator 103 creates a plurality ofcavities (e.g., 2 through 12 or more) along the axial length of theprogressive cavity pump 100. The cavities progress along the axiallength of the progressive cavity pump 100 as the rotor 104 rotateswithin the stator 103. Contact of the rotor 106 with the elastomericmaterial 109 of the stator 103 creates an interference fit that can varydepending on the operations conditions. The design of the stator 103 androtor 106 is independent of thermal effects. The combination of atapered rotor 106 and a stator 103 with a hyperboloidal bore providesthe ability to adjust the sealing between cavities and account forthermal expansion. A difference in fit between the rotor 106 and stator103 allows axial displaced to adjust for these effects. The rotor 106may be configured to allow for movement in the direction of thelongitudinal axis of the rotor 106, thereby allowing the relativeposition of the rotor 106 to be changed with respect to the stator 103.

The adjustment between the rotor 106 and stator 103 fit can be mademanually or automatically and can account for variations in operatingconditions. For example, the fit between the rotor 106 and theelastomeric material 109 could be increased to achieve increased pumpingefficiency, if the elastomeric material 109 has worn. In otherimplementations, if an operation temporarily swells the elastomericmaterial 109, such as an increase in the fluid temperature, the rotor106 can be adjusted for a looser fit to allow for the swelling and thenreadjusted to a desired fit after the swelling subsides. In addition, itmay be desirable to adjust the interference fit to allow for the passageof various fluids, such as fluids containing particulate matter. In somecases, the interference fit may be adjusted to prevent the operatingpressures from becoming excessive. By knowing the characteristics of therotor and stator (e.g., wear rate of materials), the wear can bepredicted and used to position the rotor 106 to extend the operationallife of the progressive cavity pump 100. In some cases, the position ofthe rotor 106 with respect to the stator 103 may be automaticallycarried out the extend life of the progressive cavity pump 100.

Referring next to FIG. 3, shown is a graphical representation of anexample of a progressive cavity pump 100 mounted downhole in a wellbore.A wellbore 303 can be formed in the ground for a variety ofapplications. Generally, the wellbore 303 includes a casing 306 tostabilize the hole in the ground. The progressive cavity pump 100 ispositioned within the wellbore 303 and coupled with a drive motor 309through, e.g., a gearbox 312 and a drive shaft 315. In some embodiments,the drive motor 309 may be directly coupled to the drive shaft 315. Thedrive shaft 315 may be flexibly coupled to the rotor 106 (FIG. 1) of theprogressive cavity pump 100 to allow for the skew of the rotor 106. Forexample, the drive shaft 315 may be coupled to the rotor 106 of theprogressive cavity pump 100 through one or more universal joints. Thedrive shaft 315 may also allow for axial adjustment of the rotor 106within the stator 103 (FIG. 1) of the progressive cavity pump 100.

If the progressive cavity pump 100 is used as a pump, generally thewellbore 303 contains some amount of fluid 318. In many cases, theprogressive cavity pump 100 can be configured to operate as asubmersible pump. Openings at one end of the progressive cavity pump 100allow fluid to enter the suction side 115 (FIG. 1) of the pump 100.Rotation of the rotor 106 with respect to the non-rotating stator 103produces relative motion, which pumps the fluid 318 from the lowpressure suction side 115 to a higher pressure discharge side 118(FIG. 1) of the progressive cavity pump 100. A discharge casing (orpipe) 321 is inserted down the wellbore 303 to direct fluids dischargedfrom the progressive cavity pump 100 out of the wellbore 303. Thedischarge casing 321 includes an outlet port 324 through which the fluidis directed out of the discharge casing 321.

Fluid 318 can be pumped up the wellbore 303 through the progressivecavities formed between the stator 103 and the rotor 106 and thenthrough the discharge casing 321 and out the outlet port 324.Alternatively, fluid may be pumped downhole by entering the outlet port324, moving the fluid down the discharge casing 321 and through theprogressive cavity pump 100. If the progressive cavity pump 100 is usedas a downhole motor, the discharge casing 321 may be used to flow fluiddownward through the progressive cavity pump 100. The rotor 106 would becoupled to a drive shaft (not shown) for operating downhole equipmentsuch as, e.g., mills and drill bits.

As mentioned above, the elastomeric material 109 can includefluoro-based elastomers such as, e.g., fluoromonomers and/orfluoropolymers (e.g., from DuPont) that may be used to improve operationof the progressive cavity pump 100. Embodiments of various types offluoropolymer are described herein. In particular, embodiments of thepresent disclosure can have a low coefficient of friction (e.g., about0.2 to about 0.4) and very low wear rate (e.g., about 1×10⁻⁷ mm³/Nm toabout 1×10⁻⁸ mm³/Nm, or less). In addition, embodiments of the presentdisclosure provide for elastomeric material 109 that is resistant tochemicals, have a high strength, are biocompatible, are water resistant,and/or have high thermal resistance (e.g., withstand extremetemperatures).

In an exemplary embodiment, the elastomeric material 109 can include alubricant and one or more filler components (e.g., a filler and othermaterials that may be present in the filler component). In anembodiment, the lubricant can be about 5 to 95 weight % or about 75 to95 weight % of the mixture. In an embodiment, the filler component canbe about 5 to 95 weight % or about 5 to 25 weight % of the mixture. Inan embodiment, the filler component can be about 5 to 25 weight % of themixture and the lubricant is about 75 to 95 weight % of the mixture.

Embodiments of the filler can be a filler particle such as: mullite (twostoichiometric forms 3Al₂O₃2SiO₂ or 2Al₂O₃SiO₂), pyrophyllite(Al₂Si₄O₁₀(OH)₂), kyanite (Al₂O₃.SiO₂), dolomite (CaMg(CO₃)₂), or acombination thereof. In an embodiment, the filler particle can have oneor more dimensions (e.g., diameter, length, width, height) on thenanometer scale (e.g., about 1 to 500 nm) to the micrometer scale (e.g.,about 500 nm to 500 micrometers. In an embodiment, the filler particlescan have a mixture of sizes, where, for example, some of the particlesare about 1 to 500 nm along the longest dimension and other particlesare about 1 micrometer to about 500 micrometers along the longestdimension.

In an embodiment, the filler component can include other materials suchas minerals, clays, silicates, sepiolite, kaolinite, halloysite,clinochlore, vermiculiate, chamosite, astrophylilite, clinochlore,glauconite, muscovite, talc, bauxite, quartz, mica, cristobalite,tremolite, and a combination thereof. In an embodiment, the othermaterial(s) present can be or sum up to, if more than one is present,about 0.01 to 60 weight % of the filler component. In an embodiment, theother material can be removed so that the filler(s) is at a higherpercentage of the mixture. In an embodiment, the other material can havea dimension (e.g., diameter) on the nanometer scale to the micrometerscale, or include a mixture of sizes of particles.

In an embodiment, the filler can be pyrophyllite, which can be purchasedfrom R. T. Vanderbilt Company, Inc. (i.e., composition: <40 wt %pyrophyllite with impurities of quartz (50-60 wt %), mica (18-25 wt %)and kaolin clay (5-10 wt %), where quartz, mica and kaolin clay can bethe other materials).

In an embodiment of the elastomeric material 109, where the fillercomponent is pyrophyllite and the lubricant is PTFE, elastomericmaterial 109 can have a coefficient of friction of about 0.22 to 0.26and can have a wear rate of about 5×10⁻⁷ mm³/Nm or less. The fillercomponent can be about 5 wt % of the mixture and the lubricant can beabout 95 wt % of the mixture.

In an embodiment, the filler can be mullite, which can be purchased fromKyanite Mining Corporation (i.e., composition: 75-85 wt % mullite withimpurities of amorphous silica (glass) (5-10 wt %) quartz (1-5 wt %),kyanite (1-5 wt %) and cristobalite (1-5 wt %), wherein quartz, kyanite,and cristobalite can be the other materials).

In an embodiment of elastomeric material 109, where the filler ismullite and the lubricant is PTFE, elastomeric material 109 can have acoefficient of friction of about 0.25 to 0.29 and can have a wear rateof about 4×10⁻⁷ mm³/Nm or less. The filler component can be about 5 wt %of the mixture and the lubricant can be about 95 wt % of the mixture.

In an embodiment, the filler can be dolomite, which can be purchasedfrom Specialty Minerals Inc. (i.e., composition: 60-100 wt % dolomitewith <1% quartz and <1 wt % tremolite, wherein quartz and tremolie canbe the other materials).

In an embodiment of the elastomeric material 109, where the filler isdolomite and the lubricant is PTFE, the elastomeric material 109 canhave a coefficient of friction of about 0.29 to 0.33 and can have a wearrate of about 9.3×10⁻⁸ mm³/Nm or less. The filler component can be about10 wt % of the mixture and the lubricant can be about 90 wt % of themixture.

In an embodiment, the filler can be kyanite, which can be purchased fromKyanite Mining Corporation (i.e., composition: 85-95 wt % kyanite withimpurities of quartz (5-10 wt %), titanium dioxide (1-5 wt %), andcristobalite (<0.1%), where quartz, titanium dioxide, and cristobalite,can be the other materials).

In an embodiment of the elastomeric material 109, where the filler iskyanite and the lubricant is PTFE, the elastomeric material 109 can havea coefficient of friction of about 0.3 to 0.34 and can have a wear rateof about 4×10⁻⁷ mm³/Nm or less. The filler component can be about 5 wt %of the mixture and the lubricant can be about 95 wt % of the mixture.

As mentioned above, the elastomeric material 109 can include a lubricantsuch as a fluoropolymer. Embodiments of various types of fluoropolymerare described herein.

In an embodiment, an individual fluoropolymer can be used alone;mixtures or blends of two or more different kinds of fluoropolymers canbe used as well. Fluoropolymers useful in the practice of thisdisclosure are prepared from at least one unsaturated fluorinatedmonomer (fluoromonomer). A fluoromonomer suitable for use hereinpreferably contains about 35 wt % or more fluorine, and preferably about50 wt % or more fluorine, and can be an olefinic monomer with at leastone fluorine or fluoroalkyl group or fluoroalkoxy group attached to adoubly-bonded carbon. In one embodiment, a fluoromonomer suitable foruse herein is tetrafluoroethylene (TFE).

In one embodiment, the fluoropolymer can be polytetrafluoroethylene(PTFE), which refers to (a) polymerized tetrafluoroethylene by itselfwithout any significant comonomer present, i.e. a homopolymer of TFE,and (b) modified PTFE, which is a copolymer of TFE with such smallconcentrations of comonomer that the melting point of the resultantpolymer is not substantially reduced below that of PTFE (reduced, forexample, by about 8% or less, about 4% or less, about 2% or less, orabout 1% or less). Modified PTFE contains a small amount of comonomermodifier that improves film forming capability during baking (fusing).Comonomers useful for such purpose typically are those that introducebulky side groups into the molecule, and specific examples of suchmonomers are described below. The concentration of such comonomer ispreferably less than 1 wt %, and more preferably less than 0.5 wt %,based on the total weight of the TFE and comonomer present in the PTFE.A minimum amount of at least about 0.05 wt % comonomer is preferablyused to have a significant beneficial effect on processability. Thepresence of the comonomer is believed to cause a lowering of the averagemolecular weight.

PTFE (e.g., and modified PTFE) typically have a melt creep viscosity ofat least about 1×10⁶ Pa·s and preferably at least about 1×10⁸ Pa·s. Withsuch high melt viscosity, the polymer does not flow in the molten stateand therefore is not a melt-processible polymer. The measurement of meltcreep viscosity is disclosed in col. 4 of U.S. Pat. No. 7,763,680, whichis incorporated herein by reference. The high melt viscosity of PTFEarises from its extremely high molecular weight (Mn), e.g. at leastabout 10⁶. Additional indicia of this high molecular weight include thehigh melting temperature of PTFE, which is at least 330° C., usually atleast 331° C. and most often at least 332° C. (all measured on firstheat). The non-melt flowability of the PTFE, arising from its extremelyhigh melt viscosity, manifests itself as a melt flow rate (MFR) of 0when measured in accordance with ASTM D 1238-10 at 372° C. and using a 5kg weight. This high melt viscosity also leads to a much lower heat offusion obtained for the second heat (e.g. up to 55 J/g) as compared tothe first heat (e.g. at least 75 J/g) to melt the PTFE, representing adifference of at least 20 J/g. The high melt viscosity of the PTFEreduces the ability of the molten PTFE to recrystallize upon coolingfrom the first heating. The high melt viscosity of PTFE enables itsstandard specific gravity (SSG) to be measured, which measurementprocedure (ASTM D 4894-07, also described in U.S. Pat. No. 4,036,802,which is incorporated herein by reference) includes sintering the SSGsample free standing (without containment) above its melting temperaturewithout change in dimension of the SSG sample. The SSG sample does notflow during the sintering.

Low molecular weight PTFE is commonly known as PTFE micropowder, whichdistinguishes it from the PTFE described above. The molecular weight ofPTFE micropowder is low relative to PTFE, i.e. the molecular weight (Mn)is generally in the range of 10⁴ to 10⁵. The result of this lowermolecular weight of PTFE micropowder is that it has fluidity in themolten state, in contrast to PTFE which is not melt flowable. The meltflowability of PTFE micropowder can be characterized by a melt flow rate(MFR) of at least about 0.01 g/10 min, preferably at least about 0.1g/10 min, more preferably at least about 5 g/10 min, and still morepreferably at least about 10 g/10 min., as measured in accordance withASTM D 1238-10, at 372° C. using a 5 kg weight on the molten polymer.

While PTFE micropowder is characterized by melt flowability because ofits low molecular weight, the PTFE micropowder by itself is not meltfabricable, i.e. an article molded from the melt of PTFE micropowder hasextreme brittleness, and an extruded filament of PTFE micropowder, forexample, is so brittle that it breaks upon flexing. Because of its lowmolecular weight (relative to non-melt-flowable PTFE), PTFE micropowderhas no strength, and compression molded plaques for tensile or flextesting generally cannot be made from PTFE micropowder because theplaques crack or crumble when removed from the compression mold, whichprevents testing for either the tensile property or the MIT Flex Life.Accordingly, the micropowder is assigned zero tensile strength and anMIT Flex Life of zero cycles. In contrast, PTFE is flexible, rather thanbrittle, as indicated for example by an MIT flex life [ASTMD-2176-97a(2007)], using an 8 mil (0.21 mm) thick compression moldedfilm] of at least 1000 cycles, preferably at least 2000 cycles. As aresult, PTFE micropowder finds use as a blend component with otherpolymers such as PTFE itself and/or copolymers of TFE with othermonomers such as those described below.

In other embodiments, a fluoromonomer suitable for use herein, by itselfto prepare a homopolymer or in copolymerization with other comonomerssuch as TFE, can be represented by the structure of the followingFormula I:

where R¹ and R² are each independently selected from H, F and Cl; R³ isH, F, or a C₁˜C₁₂, or C₁˜C₈, or C₁˜C₆, or C₁˜C₄ straight-chain orbranched, or a C₃˜C₁₂, or C₃˜C₈, or C₃˜C₆ cyclic, substituted orunsubstituted, alkyl radical; R⁴ is a C₁˜C₁₂, or C₁˜C₈, or C₁˜C₆, orC₁˜C₄ straight-chain or branched, or a C₃˜C₁₂, or C₃˜C₈, or C₃˜C₆cyclic, substituted or unsubstituted, alkylene radical; A is H, F or afunctional group; a is 0 or 1; and j and k are each independently 0 to10; provided that, when a, j and k are all 0, at least one of R¹, R², R³and A is not F.

An unsubstituted alkyl or alkylene radical as described above containsno atoms other than carbon and hydrogen. In a substituted hydrocarbylradical, one or more halogens selected from Cl and F can be optionallysubstituted for one or more hydrogens; and/or one or more heteroatomsselected from O, N, S and P can optionally be substituted for any one ormore of the in-chain (i.e. non-terminal) or in-ring carbon atoms,provided that each heteroatom is separated from the next closestheteroatom by at least one and preferably two carbon atoms, and that nocarbon atom is bonded to more than one heteroatom. In other embodiments,at least 20%, or at least 40%, or at least 60%, or at least 80% of thereplaceable hydrogen atoms are replaced by fluorine atoms. Preferably aFormula I fluoromonomer is perfluorinated, i.e. all replaceable hydrogenatoms are replaced by fluorine atoms.

In a Formula I compound, a linear R³ radical can, for example, be aC_(b) radical where b is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 and theradical can contain from 1 up to 2b+1 fluorine atoms. For example, a C₄radical can contain from 1 to 9 fluorine atoms. A linear R³ radical isperfluorinated with 2b+1 fluorine atoms, but a branched or cyclicradical will be perfluorinated with fewer than 2b+1 fluorine atoms. In aFormula I compound, a linear R⁴ radical can, for example, be a C_(c)radical where c is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 and theradical can contain from 1 to 2c fluorine atoms. For example, a C₆radical can contain from 1 to 12 fluorine atoms. A linear R⁴ radical isperfluorinated with 2c fluorine atoms, but a branched or cyclic radicalwill be perfluorinated with fewer than 2c fluorine atoms.

Examples of a C₁˜C₁₂ straight-chain or branched, substituted orunsubstituted, alkyl or alkylene radical suitable for use herein caninclude or be derived from a methyl, ethyl, n-propyl, i-propyl, n-butyl,sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl, trimethylpentyl,allyl and propargyl radical. Examples of a C₃˜C₁₂ cyclic aliphatic,substituted or unsubstituted, alkyl or alkylene radical suitable for useherein can include or be derived from an alicyclic functional groupcontaining in its structure, as a skeleton, cyclohexane, cyclooctane,norbornane, norbornene, perhydro-anthracene, adamantane, ortricyclo-[5.2.1.0^(2.6)]-decane groups.

Functional groups suitable for use herein as the A substituent inFormula I include ester, alcohol, acid (including carbon-, sulfur-, andphosphorus-based acid) groups, and the salts and halides of such groups;and cyanate, carbamate, and nitrile groups. Specific functional groupsthat can be used include —SO₂F, —CN, —COOH, and —CH₂—Z wherein —Z is—OH, —OCN, —O—(CO)—NH₂, or —OP(O)(OH)₂.

Formula I fluoromonomers that can be homopolymerized include vinylfluoride (VF), to prepare polyvinyl fluoride (PVF), and vinylidenefluoride (VF₂) to prepare polyvinylidene fluoride (PVDF), andchlorotrifluoroethylene to prepare polychlorotrifluoroethylene. Examplesof Formula I fluoromonomers suitable for copolymerization include thosein a group such as ethylene, propylene, 1-butene, 1-hexene, 1-octene,chlorotrifluoroethylene (CTFE), trifluoroethylene,hexafluoroisobutylene, vinyl fluoride (VF), vinylidene fluoride (VF₂),and perfluoroolefins such as hexafluoropropylene (HFP), andperfluoroalkyl ethylenes such as perfluoro(butyl) ethylene (PFBE). Apreferred monomer for copolymerization with any of the above namedcomonomers is tetrafluoroethylene (TFE).

In yet other embodiments, a fluoromonomer suitable for use herein, byitself to prepare a homopolymer or in copolymerization with TFE and/orany of the other comonomers described above, can be represented by thestructure of the following Formula II:

wherein R¹ through R³ and A are each as set forth above with respect toFormula I; d and e are each independently 0 to 10; f, g and h are eachindependently 0 or 1; and R⁵ through R⁷ can each be selected from thesame radicals as described above with respect to R⁴ in Formula I exceptthat when d and e are both non-zero and g is zero, R⁵ and R⁶ aredifferent R⁴ radicals.

Formula II compounds introduce ether functionality into fluoropolymerssuitable for use herein, and include fluorovinyl ethers such as thoserepresented by the following formula:CF₂═CF—(O—CF₂CFR¹¹)_(h)—O—CF₂CFR¹²SO₂F, where R¹¹ and R¹² are eachindependently selected from F, Cl, or a perfluorinated alkyl grouphaving 1 to 10 carbon atoms, and h=0, 1 or 2. Examples of polymers ofthis type that are disclosed in U.S. Pat. No. 3,282,875 includeCF₂═CF—O—CF₂CF(CF₃)—O—CF₂CF₂SO₂F andperfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride), and examplesthat are disclosed in U.S. Pat. Nos. 4,358,545 and 4,940,525 includeCF₂═CF—O—CF₂CF₂SO₂F. Another example of a Formula II compound isCF₂═CF—O—CF₂—CF(CF₃)—O—CF₂CF₂CO₂CH₃, the methyl ester ofperfluoro(4,7-dioxa-5-methyl-8-nonenecarboxylic acid), as disclosed inU.S. Pat. No. 4,552,631. Similar fluorovinyl ethers with functionalityof nitrile, cyanate, carbamate, and phosphonic acid are disclosed inU.S. Pat. Nos. 5,637,748, 6,300,445 and 6,177,196. Methods for makingfluoroethers suitable for use herein are set forth in the U.S. patentslisted above in this paragraph, and each of the U.S. patents listedabove in this paragraph is by this reference incorporated in itsentirety as a part hereof for all purposes.

Particular Formula II compounds suitable for use herein as a comonomerinclude fluorovinyl ethers such as perfluoro(allyl vinyl ether) andperfluoro(butenyl vinyl ether). Preferred fluorovinyl ethers includeperfluoro(alkyl vinyl ethers) (PAVE), where the alkyl group contains 1to 5 carbon atoms, with perfluoro(ethyl vinyl ether) (PEVE) andperfluoro(propyl vinyl ether) (PPVE), and perfluoro(methyl vinyl ether)(PMVE) being preferred.

In yet other embodiments, a fluoromonomer suitable for use herein, byitself to prepare a homopolymer or in copolymerization with TFE and/orany of the other comonomers described above, can be represented by thestructure of the following Formula III:

where each R³ is independently as described above in relation to FormulaI. Suitable Formula III monomers includeperfluoro-2,2-dimethyl-1,3-dioxole (PDD).

In yet other embodiments, a fluoromonomer suitable for use herein, byitself to prepare a homopolymer or in copolymerization with TFE and/orany of the other comonomers described above, can be represented by thestructure of the following Formula IV:

where each R³ is independently as described above in relation to FormulaI. Suitable Formula IV monomers includeperfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD).

In various embodiments, fluoropolymer copolymers suitable for use hereincan be prepared from any two, three, four or five of these monomers: TFEand a Formula I, II, III and IV monomer. The following are thusrepresentative combinations that are available: TFE/Formula I;TFE/Formula II; TFE/Formula III; TFE/Formula IV; TFE/Formula I/FormulaII; TFE/Formula I/Formula III; TFE/Formula I/Formula IV; FormulaI/Formula II; Formula I/Formula III; and Formula I/Formula IV. Providedthat at least two of the five kinds of monomers are used, a unit derivedfrom each monomer can be present in the final copolymer in an amount ofabout 1 wt % or more, or about 5 wt % or more, or about 10 wt % or more,or about 15 wt % or more, or about 20 wt % or more, and yet no more thanabout 99 wt %, or about 95 wt % or less, or about 90 wt % or less, orabout 85 wt % or less, or about 80 wt % or less (based on the weight ofthe final copolymer); with the balance being made up of one, two, threeor all of the other five kinds of monomers.

A fluoropolymer as used herein can also be a mixture of two or more ofthe homo- and/or copolymers described above, which is usually achievedby dry blending. A fluoropolymer as used herein can also, however, be apolymer alloy prepared from two or more of the homo- and/or copolymersdescribed above, which can be achieved by melt kneading the polymertogether such that there is mutual dissolution of the polymer, chemicalbonding between the polymers, or dispersion of domains of one of thepolymers in a matrix of the other.

Tetrafluoroethylene polymers suitable for use herein can be produced byaqueous polymerization (as described in U.S. Pat. No. 3,635,926) orpolymerization in a perhalogenated solvent (U.S. Pat. No. 3,642,742) orhybrid processes involving both aqueous and perhalogenated phases (U.S.Pat. No. 4,499,249). Free radical polymerization initiators and chaintransfer agents are used in these polymerizations and have been widelydiscussed in the literature. For example, persulfate initiators andalkane chain transfer agents are described for aqueous polymerization ofTFE/PAVE copolymers. Fluorinated peroxide initiators and alcohols,halogenated alkanes, and fluorinated alcohols are described fornonaqueous or aqueous/nonaqueous hybrid polymerizations.

Various fluoropolymers suitable for use herein include those that arethermoplastic, which are fluoropolymers that, at room temperature, arebelow their glass transition temperature (if amorphous), or below theirmelting point (if semi-crystalline), and that become soft when heatedand become rigid again when cooled without the occurrence of anyappreciable chemical change. A semi-crystalline thermoplasticfluoropolymer can have a heat of fusion of about 1 J/g or more, or about4 J/g or more, or about 8 J/g or more, when measured by DifferentialScanning calorimetry (DSC) at a heating rate of 10° C./min (according toASTM D 3418-08).

Various fluoropolymers suitable for use herein can additionally oralternatively be characterized as melt-processible, and melt-processiblefluoropolymers can also be melt-fabricable. A melt-processiblefluoropolymer can be processed in the molten state, i.e. fabricated fromthe melt using conventional processing equipment such as extruders andinjection molding machines, into shaped articles such as films, fibersand tubes. A melt-fabricable fluoropolymer can be used to producefabricated articles that exhibit sufficient strength and toughness to beuseful for their intended purpose despite having been processed in themolten state. This useful strength is often indicated by a lack ofbrittleness in the fabricated article, and/or an MIT Flex Life of atleast about 1000 cycles, or at least about 2000 cycles (measured asdescribed above), for the fluoropolymer itself.

Examples of thermoplastic, melt-processible and/or melt-fabricablefluoropolymers include copolymers of tetrafluoroethylene (TFE) and atleast one fluorinated copolymerizable monomer (comonomer) present in thepolymer in sufficient amount to reduce the melting point of thecopolymer below that of PTFE, e.g. to a melting temperature no greaterthan 315° C. Such a TFE copolymer typically incorporates an amount ofcomonomer into the copolymer in order to provide a copolymer which has amelt flow rate (MFR) of at least about 1, or at least about 5, or atleast about 10, or at least about 20, or at least about 30, and yet nomore than about 100, or no more than about 90, or no more than about 80,or no more than about 70, or no more than about 60, as measuredaccording to ASTM D-1238-10 using a weight on the molten polymer andmelt temperature which is standard for the specific copolymer.Preferably, the melt viscosity is at least about 10² Pa·s, morepreferably, will range from about 10² Pa·s to about 10⁶ Pa·s, mostpreferably about 10³ to about 10⁵ Pa·s. Melt viscosity in Pa·s is531,700/MFR in g/10 min.

In general, thermoplastic, melt-processible and/or melt-fabricablefluoropolymers as used herein include copolymers that contain at leastabout 40 mol %, or at least about 45 mol %, or at least about 50 mol %,or at least about 55 mol %, or at least about 60 mol %, and yet no morethan about 99 mol %, or no more than about 90 mol %, or no more thanabout 85 mol %, or no more than about 80 mol %, or no more than about 75mol % TFE; and at least about 1 mol %, or at least about 5 mol %, or atleast about 10 mol %, or at least about 15 mol %, or at least about 20mol %, and yet no more than about 60 mol %, or no more than about 55 mol%, or no more than about 50 mol %, or no more than about 45 mol %, or nomore than about 40 mol % of at least one other monomer. Suitablecomonomers to polymerize with TFE to form melt-processiblefluoropolymers include a Formula I, II, III and/or IV compound; and, inparticular, a perfluoroolefin having 3 to 8 carbon atoms [such ashexafluoropropylene (HFP)], and/or perfluoro(alkyl vinyl ethers) (PAVE)in which the linear or branched alkyl group contains 1 to 5 carbonatoms.

Preferred PAVE monomers are those in which the alkyl group contains 1,2, 3 or 4 carbon atoms, and the copolymer can be made using several PAVEmonomers. Preferred TFE copolymers include FEP (TFE/HFP copolymer), PFA(TFE/PAVE copolymer), TFE/HFP/PAVE wherein PAVE is PEVE and/or PPVE, MFA(TFE/PMVE/PAVE wherein the alkyl group of PAVE has at least two carbonatoms) and THV (TFE/HFP/VF₂). Additional melt-processible fluoropolymersare the copolymers of ethylene (E) or propylene (P) with TFE orchlorinated TFE (CTFE), notably ETFE, ECTFE and PCTFE. Also useful inthe same manner are film-forming polymers of polyvinylidene fluoride(PVDF) and copolymers of vinylidene fluoride as well as polyvinylfluoride (PVF) and copolymers of vinyl fluoride.

Fluoropolymers that are thermoplastic, melt-processible and/ormelt-fabricable are in general characterized by a melt flow rate asdescribed above, and can be distinguished from fluoroelastomers, whichtypically have a glass transition temperature below about 25° C.,exhibit little or no crystallinity at room temperature, and/or have acombination of low flex modulus, high elongation, and rapid recoveryfrom deformation. Fluoroelastomers can also be characterized, in variousapplications, by the definition in ASTM Special Technical Bulletin No.184 under which they can be stretched (at room temperature) to twicetheir intrinsic length, and, once released after being held undertension for 5 minutes, return to within 10% of their initial length inthe same time.

Fluoropolymers suitable for use herein thus also includefluoroelastomers (fluorocarbon elastomers), which typically contain atleast about 25 wt %, or at least about 35 wt %, or at least about 45 wt%, and yet no more than about 70 wt %, or no more than about 60 wt %, orno more than about 50 wt % (based on the total weight of thefluoroelastomer), of a first copolymerized fluorinated monomer such asvinylidene fluoride (VF₂) or TFE; with the remaining copolymerized unitsin the fluoroelastomer being selected from other, differentfluoro-monomers such as a Formula I, II, III and/or IV compound; and, inparticular, hydrocarbon olefins. Fluoroelastomers may also, optionally,comprise units of one or more cure site monomers. When present,copolymerized cure site monomers are typically at a level of 0.05 to 7wt %, based on total weight of fluorocarbon elastomer. Examples ofsuitable cure site monomers include: (i) bromine-, iodine-, orchlorine-containing fluorinated olefins or fluorinated vinyl ethers;(ii) nitrile group-containing fluorinated olefins or fluorinated vinylethers; (iii) perfluoro(2-phenoxypropyl vinyl ether); and (iv)non-conjugated dienes.

Preferred TFE-based fluoroelastomer copolymers include TFE/PMVE,TFE/PMVE/E, TFE/P and TFE/P/VF₂. Preferred VF₂ based fluorocarbonelastomer copolymers include VF₂/HFP, VF₂/HFP/TFE, and VF₂/PMVE/TFE. Anyof these elastomer copolymers may further comprise units of cure sitemonomer.

Embodiments of the progressive cavity pump 100 including an elastomericmaterial 109 such as fluoropolymers (e.g., including the lubricant and afiller) can be made using any suitable processing technique that resultsin an elastomeric material 109 coating comprising the fluoropolymermatrix, which can include alumina and silica particles dispersedtherein.

For example, embodiments based on fluoropolymers that are not meltprocessible can be made by a sintering or molding technique, in whichthe components are first mixed (e.g., by mechanical mixing, dispersionin a liquid, or other forms of mixing). The mixture is then transferredto a molding chamber where it is consolidated with pressure. In animplementation, the molding can be done at a pressure of about 20 to 200MPa for about 10 seconds to 10 minutes and thereafter the fluoropolymercan be heated to above its melting point, held for a period of time(e.g., about 10 minutes to 10 hrs) to permit the fluoropolymer tosinter, and then cooled to ambient temperature. The sintering operationcan be carried out under continued application of compression(denominated herein as “compression molding”) or as a free sintering,i.e., without continued application of a compressive force. One possibleimplementation of a free sintering manufacture is set forth in ASTMStandard No. 1238-10. In other implementations, the consolidation iscarried out at a pressure of about 20 to 250 MPa for a time of about 10sec to 10 min. The sintering may be accomplished by ramping thetemperature at a rate of about 2° C. per minute to a preselectedtemperature of about 360° C. to 390° C. and held for a period of about 1to 10 hrs) and then cooled (e.g., at about 2° C. per minute) down toroom temperature. Optionally, the compressive pressure is maintainedduring the sintering.

Other methods of making the coating are also contemplated within thescope of the present disclosure. For example, alternative embodimentsprovide fluoropolymer composite bodies formed by melt processing thecomposite powder material. In some implementations, the melt processingcomprises a multistage process, in which an intermediate is firstproduced in the form of powder, granules, pellets, or the like, andthereafter remelted and formed into an article of manufacture having adesired final shape. In an implementation, the intermediate is formed bya melt compounding or blending operation that comprises transformationof a thermoplastic resin from a solid pellet, granule or powder into amolten state by the application of thermal or mechanical energy.Requisite additive materials, such as composite powder material bearingfluoropolymers and particle additives (e.g., silica and alumina)prepared as described herein, may be introduced during the compoundingor mixing process, before, during, or after the polymer matrix has beenmelted or softened. The compounding equipment then provides sufficientmechanical energy to provide sufficient stress to disperse theingredients in the compositions, move the polymer, and distribute theadditives to form a homogeneous mixture.

Melt blending can be accomplished with batch mixers (e.g., mixersavailable from Haake, Brabender, Banbury, DSM Research, and othermanufacturers) or with continuous compounding systems, which may employextruders or planetary gear mixers. Suitable continuous processequipment includes co-rotating twin screw extruders, counter-rotatingtwin screw extruders, multi-screw extruders, single screw extruders,co-kneaders (reciprocating single screw extruders), and other equipmentdesigned to process viscous materials. Batch and continuous processinghardware suitable for carrying out steps of the present method mayimpart sufficient thermal and mechanical energy to melt specificcomponents in a blend and generate sufficient shear and/or elongationalflows and stresses to break solid particles or liquid droplets and thendistribute them uniformly in the major (matrix) polymer melt phase.Ideally, such systems are capable of processing viscous materials athigh temperatures and pumping them efficiently to downstream forming andshaping equipment. It is desirable that the equipment also be capable ofhandling high pressures, abrasive wear and corrosive environments.Compounding systems used in the present method typically pump aformulation melt through a die and pelletizing system.

The intermediate may be formed into an article of manufacture having adesired shape using techniques such as injection molding, blow molding,extruded film casting, blown film, fiber spinning, stock shapeextrusion, pipe and tubing extrusion, thermoforming, compressionmolding, or the like, accomplished using suitable forming equipment.Such embodiments may require that the fluoropolymer powder particlesused to form the slurry and composite powder material be composed of amelt-processible fluoropolymer.

In other implementations, material produced by the melt-blending orcompounding step is immediately melt processed into a desired shape,without first being cooled or formed into powder, granules, or the like.For example, in-line compounding and injection molding systems combinetwin-screw extrusion technology in an injection molding machine so thatthe matrix polymer and other ingredients experience only one melthistory.

In other embodiments, materials produced by shaping operations,including melt processing and forming, compression molding or sintering,may be machined into final shapes or dimensions. In still otherimplementations, the surfaces of the parts may be finished by polishingor other operations.

In still other embodiments, the composite powder material can be used asa carrier material by which the particles (e.g., filler) are introducedinto a matrix that may include an additional amount of the samefluoropolymer used in the composite powder material, one or more otherfluoropolymers, or both. For example, the composite powder material maybe formed using the present slurry technique with a first fluoropolymerpowder material that is not melt-processible, with the intermediatethereafter blended with a second, melt-processible fluoropolymer powder.In an embodiment, the proportions of the two polymers are such that theoverall blend is melt-processible. Other embodiments may entail morethan two blended fluoropolymers.

Alternatively, the intermediate can be formed with a non-meltprocessible fluoropolymer and thereafter combined with more of the samefluoropolymer and processed by compression molding and sintering.

It should also be noted that the tribological properties of articles ofthe present disclosure can be designed for a particular application.Thus, embodiments of the present disclosure can provide articles thatcan satisfy many different requirements for different industries and forparticular components.

It should be emphasized that the above-described embodiments of thepresent disclosure are merely possible examples of implementations setforth for a clear understanding of the principles of the disclosure.Many variations and modifications may be made to the above-describedembodiment(s) without departing substantially from the spirit andprinciples of the disclosure. All such modifications and variations areintended to be included herein within the scope of this disclosure andprotected by the following claims.

It should be noted that ratios, concentrations, amounts, and othernumerical data may be expressed herein in a range format. It is to beunderstood that such a range format is used for convenience and brevity,and thus, should be interpreted in a flexible manner to include not onlythe numerical values explicitly recited as the limits of the range, butalso to include all the individual numerical values or sub-rangesencompassed within that range as if each numerical value and sub-rangeis explicitly recited. To illustrate, a concentration range of “about0.1% to about 5%” should be interpreted to include not only theexplicitly recited concentration of about 0.1 wt % to about 5 wt %, butalso include individual concentrations (e.g., 1%, 2%, 3%, and 4%) andthe sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within theindicated range. The term “about” can include traditional roundingaccording to significant figures of numerical values. In addition, thephrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”.

Therefore, at least the following is claimed:
 1. A progressive cavitypump, comprising: a stator having a hyperboloidal internal boreincluding a plurality of spiral lobes; and a rotor comprising aplurality of spiral lobes positioned within the hyperboloidal internalbore of the stator, where a longitudinal axis of the rotor isnon-planar, non-parallel, and non-intersecting with a longitudinal axisof the stator.
 2. The progressive cavity pump of claim 1, wherein thelongitudinal axis of the rotor is offset from the longitudinal axis ofthe stator and rotated by a defined angle.
 3. The progressive cavitypump of claim 2, wherein the defined angle is in a range from about0.001 degree to about 10 degrees.
 4. The progressive cavity pump ofclaim 2, wherein the longitudinal axis of the rotor is offset from thelongitudinal axis of the stator by a defined distance.
 5. Theprogressive cavity pump of claim 4, wherein the defined distance is in arange from about 0.01 inch to about 10 inches.
 6. The progressive cavitypump of claim 2, wherein skew axes of the stator and rotor arenon-planar, non-parallel, and non-intersecting.
 7. The progressivecavity pump of claim 1, wherein the rotor is tapered from a larger endto a smaller end.
 8. The progressive cavity pump of claim 7, wherein thetaper of the rotor is hyperboloidal.
 9. The progressive cavity pump ofclaim 1, wherein the stator comprises an elastomeric material coatingthe hyperboloidal internal bore of the stator.
 10. The progressivecavity pump of claim 9, wherein the elastomeric material reduces theeffect of friction and abrasion when operating under high temperatureconditions.
 11. The progressive cavity pump of claim 10, wherein theelastomeric material comprises a fluoropolymer.
 12. The progressivecavity pump of claim 11, wherein the fluoropolymer ispolytetrafluoroethylene (PTFE).
 13. The progressive cavity pump of claim10, wherein the elastomeric material further comprises a fillercomponent.
 14. The progressive cavity pump of claim 13, wherein thefiller component comprises mullite, pyrophyllite, kyanite, dolomite, ora combination thereof.
 15. The progressive cavity pump of claim 10,wherein the elastomeric material has a coefficient of friction in therange of about 0.2 to about 0.4 and a wear rate of about 1×10⁻⁷ mm³/Nmor less.
 16. The progressive cavity pump of claim 1, wherein the rotoris configured to allow for displacement to adjust an interference fitbetween the rotor and the stator.
 17. The progressive cavity pump ofclaim 16, wherein the rotor can be displaced along the longitudinal axisof the rotor.